An urban terrorist attack involving release of biological warfare agents such as bacillus anthracis (anthrax) is presently a realistic concern. Weaponized anthrax spores are extremely dangerous because they can gain passage into the human lungs. A lethal inhalation dose of anthrax spores for humans, LD50 (lethal dose sufficient to kill 50% of the persons exposed) is estimated to be 2,500 to 50,000 spores (see T. V. Inglesby, et al., “anthrax as a Biological Weapon”, JAMA, vol. 2801, page 1735, 1999). Some other potential weaponized bio-agents are yersinia pestis (plaque), clostridium botulinum (botulism), and francisella tularensis. In view of this potential threat, there is currently a need for an early warning system to detect such an attack. In the pharmaceutical, healthcare and food industries, a real time detector of environmental microbial level is useful for public health, quality control and regulatory purposes. For example, parental drug manufacturers are required to monitor the microbial levels in their aseptic clean rooms. In these applications, an instrument which can detect microbes in the environment instantaneously will be a useful tool and have advantages over conventional nutrient plate culture methods which requires days for microbes to grow and to be detected.
Particle size measurement and ultraviolet (UV) induced fluorescence detection have been used to detect the presence of biological substances in the air. There exist various patents describing using these techniques as early warning sensors for bio-terrorist attack release of weaponized bio-agents. Among these devices are Biological Agent Warning Sensor (BAWS) developed by MIT Lincoln Laboratory, fluorescence biological particle detection system of Ho (Jim yew-Wah Ho, U.S. Pat. Nos. 5,701,012; 5,895,922; 6,831,279); FLAPS and UV-APS by TSI of Minnesota (Peter P. Hairston; and Frederick R. Quant; U.S. Pat. No. 5,999,250), and a fluorescence sensor by Silcott (U.S. Pat. No. 6,885,440).
A proposed bio-sensor based on laser-induced fluorescence using a pulsed UV laser is described by T. H. Jeys, et al., Proc. IRIS Active Systems, vol. 1, p.235, 1998. This is capable of detecting an aerosol concentration of five particles per liter of air, but involves expensive and delicate instruments. Other particle counters are manufactured by Met One Instrument, Inc, of Grants Pass, Oreg., Particle Measurement Systems, Inc., of Boulder, Colo., and Terra Universal Corp., of Anaheim, Calif.
Various detectors have been designed to detect airborne allergen particles and provide warning to sensitive individuals when the number of particles within an air sample exceeds a predetermined minimum value. These are described in U.S. Pat. Nos. 5,646,597, 5,969,622, 5,986,555, 6,008,729, 6,087,947, and 7,053,783, all to Hamburger et al. These detectors all involve direction of a light beam through a sample of environmental air such that part of the beam will be scattered by any particles in the air, a beam blocking device for transmitting only light scattered in a predetermined angular range corresponding to the predetermined allergen size range, and a detector for detecting the transmitted light.